1. Field of the Invention
This invention relates to counter circuitry and more particularly to counter circuitry for counting all transitions of two or more overlapped out of phase bi-level signals.
The invention finds particular utility in position control systems. For example, it can be used to control the operation of a stepping motor. It is not uncommon for stepping motors to operate in a fashion where out of phase emitter pulses taken from an emitter driven by the stepping motor are fed back to further drive the stepping motor. The stepping motor continues to operate until it has taken a predetermined number of steps. The counter of this invention can be used to keep track of the number of steps taken by the stepping motor. The stepping motor can be connected to position any element and, for example, could be used to operate a paper carriage for advancing continuous forms in a printer. Assume that it takes 16 steps to advance the continuous forms one line space. Then, after the printer completes a line of printing, a control unit would issue a start signal to the stepper motor. The stepper motor would step continuously until the start signal is dropped. The start signal would drop after the counter counts 16 overlapped transitions from the emitter driven by the stepper motor.
2. Description of the Prior Art
Heretofore, signal transitions of two or more overlapped out of phase bi-level signals were counted by applying the separate signals to separate counters and then the outputs of the separate counters were logically combined to provide an overall count of the transitions. In other instances a sequence detector and reversible counter are used in combination. The sequence detector logically combines the incoming signals into phase pairs and examines the sequence thereof to determine the direction for advancing the counter. Such an arrangement is represented by U.S. Pat. No. 3,165,680 dated Jan. 12, 1965, for "Digital Position Control Servosystem". Other prior art approaches utilize analog circuitry such as differential networks and clipping circuitry to develop the counter advance pulses. All of the aforementioned approaches are more complex and thus involve either more circuitry in the case of the prior art digital approaches or in the case of analog approaches require more expensive circuitry. In any event the prior art approaches are more costly than the present invention.